Process for producing hydrogen

ABSTRACT

An Mg alloy powder is reacted with water to produce hydogen. The Mg alloy powder is produced by hydrogenating an aggregate of Mg alloy particles each having an Mg particle and a plurality of catalyst metal particulates existing on a surface of and within the Mg particle. The catalyst metal particulates are at least one selected from Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates. Thus, hydrogen can be produced quickly and in large amounts, and waste liquid is easily treated. Moreover, hydrogen production cost can be reduced using an inexpensive catalyst.

BACKGROUND OF THE INVENTION

[0001] 1. FIELD OF THE INVENTION

[0002] The present invention relates to a process for producing hydrogen, and particularly to a process for producing hydrogen by the reaction of an Mg alloy powder with water.

[0003] 2. DESCRIPTION OF THE RELATED ART

[0004] There is a conventional hydrogen producing process in which sodium borohydride (NaBH₄) and a catalyst are used, and water is added to them for reaction with NaBH₄ (for example, see Japanese Patent Application Laid-open No.2001-199701).

[0005] However, the conventional process has the following problems: NaBO₂ is produced by the reaction between NaBH₄ and water, and a strong alkali aqueous solution remains as a waste liquid, such that additional labor and high costs become necessary for disposal of the waste liquid. In addition, a noble metal such as Pt, Pd and the like is used as a component of the catalyst, resulting in an increased hydrogen production cost.

SUMMARY OF THE INVENTION

[0006] Accordingly, it is an object of the present invention to provide a hydrogen producing process, in which hydrogen can be produced quickly and in a large amount; the waste liquid can be easily treated; and the hydrogen production cost can be reduced by using an inexpensive catalyst.

[0007] To achieve the above object, according to the present invention, there is provided a process for producing hydrogen by the reaction of an Mg alloy powder with water, in which the Mg alloy powder is a powder produced by hydrogenating an aggregate of Mg alloy particles each having an Mg particle and a plurality of catalyst metal particulates existing on a surface of the Mg particle and within the Mg particle, the catalyst metal particulates being at least one selected from Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.

[0008] The Mg alloy powder having the above-described structure absorbs a relatively large amount of hydrogen with a hydrogenation-promoting function provided by the catalyst metal particulates in the hydrogenating treatment.

[0009] On the other hand, the catalyst metal particulates function to form cathode portions having a low hydrogenating voltage in the Mg particles to quickly convert Mg into hydroxide [Mg(OH)₂]. Thus, the hydrolysis of MgH₂ is promoted and hence, hydrogen can be produced quickly and in a large amount. Furthermore, the waste liquid is an aqueous solution of Mg(OH)₂ and hence, is easily treated.

[0010] Moreover, the above-described catalyst metal particulates are inexpensive, as compared with a noble metal catalyst, and hence a reduction in the hydrogen production cost can be achieved.

[0011] According to the present invention, there is also provided a process for producing hydrogen by the reaction of an Mg alloy powder with water, in which the Mg alloy powder is an aggregate of Mg alloy particles each having an Mg particle and a plurality of catalyst metal particulates existing on a surface of the Mg particle and within the Mg particle, the catalyst metal particles being at least one selected from Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.

[0012] Hydrogen is produced by the reaction of a powder of pure Mg with water. However, the period of hydrogen production is extremely short, and the amount of produced hydrogen is small. The Mg alloy powder having the above-described structure continuously reacts with water by the above-described function of the catalyst metal particulates, and hence the period of hydrogen production can be extended to increase the amount of produced hydrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings, in which:

[0014]FIG. 1 is a diagram illustrating an Mg alloy particle in accordance with embodiments of this invention;

[0015]FIG. 2 is a graph showing the relationship between the time and the temperature of an Mg alloy powder under H₂ absorbing;

[0016]FIG. 3 is a graph showing the relationship between the time and the amount of hydrogen absorbed;

[0017] FIG.4 is a graph showing the relationship between the time and the amount of produced hydrogen; and

[0018]FIG. 5 is a graph showing the relationship between the time and the amount of hydrogen produced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (Embodiment I) To produce hydrogen, a process for producing hydrogen by the reaction of an Mg alloy power with water is employed. The Mg alloy powder which is used is a powder made by hydrogenating an aggregate of Mg alloy particles 3 each comprising a Mg particle 1 and a plurality of catalyst metal particulates 2 existing on a surface of the Mg particle 1 and within the Mg particle 1, as shown in FIG. 1. The catalyst metal particulates 2 correspond to at least one selected from Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.

[0020] The content G of the catalyst metal particulates 2 in the Mg alloy powder is set in a range of 0.1% by atom≦G≦5.0% by atom. If the content G is lower than 0.1% by atom, no effect is provided by addition of the catalyst metal particulates 2. On the other hand, if G>5.0% by atom, the amount of produced hydrogen is reduced and hence, a content higher than 5.0% by atom is not of practical use. The content G of the catalyst particulates 2 is preferably in a range of 0.3% by atom≦G≦1.0% by atom. The Mg alloy powder is produced under application of a mechanical alloying, and hence an appropriate particle size D of the Mg particle 1 is in a range of 1 μm≦D≦500 nm, and an appropriate particle size d of the catalyst metal particulates 2 is in a range of 10 nm≦d≦500 2nm. In this case, each of the particle sizes D and d is defined as a length of the largest portion of the Mg particle or the like in a microphotograph (a largest diameter).

[0021] Specific examples will be described below.

[0022] (A) Production of Mg Alloy Powder

[0023] The following aggregates were prepared: an aggregate of Mg particles having a purity of 99.9% and a particle size D₀ equal to or smaller than 180 μm; an aggregate of Ni particulates having a particle size d in a range of 10 nm≦d≦100 nm; and an aggregate of Fe particulates having a purity of 99.9% and a particle size d in a range of 10 nm≦d≦200 nm. These aggregates were weighed and mixed together to produce a mixed powder having an alloy composition represented by Mg₉₅Ni_(3.33)Fe_(1.67) (each of the numerical values represents % by atom).

[0024] The mixed powder was placed in a pot (made under JIS SUS316) having a volume of 2,500 ml in a horizontal ball mill (made by Honda) along with 990 balls having a diameter of 10 mm (made under JIS SUS316), and was subjected to ball milling with the interior of the pot maintained in a hydrogen gas atmosphere of 2 MPa and under conditions of a pot rotational speed of 70 rpm and a milling time t of 15 minutes. In this case, an acceleration 3G three times the gravitational acceleration G_(p) was generated in the pot. After completion of the ball milling, the produced Mg alloy powder was removed into the atmosphere. The Mg alloy powder was hydrogenated during the process of the ball milling, and hence was subjected to a dehydrogenating treatment by conducting an evacuation under conditions of 350° C. for one hour.

[0025] The Mg alloy powder was subjected to SEM and TEM observations, and as a result it found that the particle size was decreased by pulverization of the powder or increased by the agglomeration and aggregation and thus, the particle size D of the Mg particles 1 was in a range of 2 μm≦D≦300 μm. The particle size of each of the Ni and Fe particulates 2 was not decreased. It was also found in the Mg alloy particles 3 constituting the Mg alloy powder that a plurality of the Ni and Fe particulates 2 in the form of black spots exist on the surface of the Mg particle I and within the Mg particle 1.

[0026] (B) Hydrogenation of Mg Alloy Powder and Change in Temperature of the Powder

[0027] The Mg alloy powder was placed in a vessel, and then the temperature of the Mg alloy powder was constantly maintained at 250° C. Thereafter, hydrogen was introduced into the vessel, and when the internal pressure in the vessel reached up to 1 MPa, the introduction of hydrogen was terminated, and the temperature of the Mg alloy powder was no longer maintained at 250° C. Thereafter, the temperature of the Mg alloy powder was measured to provide the results shown in FIG. 2. As shown in FIG. 2, it was found that the Mg alloy powder generated heat with the hydrogenation thereof, namely, the absorption of hydrogen thereinto and as a result, the temperature of the Mg alloy powder rose up to about 310° C. in about 40 seconds after termination of the introduction of hydrogen. Therefore, it is possible to cause the Mg alloy powder to absorb hydrogen under the application of a pressure (equal to or higher than 0.1 MPa), while maintaining the temperature of the Mg alloy powder at 310° C. or lower.

[0028] (C) Hydrogenation of Mg Alloy Powder

[0029] The Mg alloy powder was placed in a vessel. Then, the temperature of the Mg alloy powder was constantly maintained at 310° C., and hydrogen was introduced into the vessel while the internal pressure in the vessel was constantly maintained at 1 MPa. In this state, the amount of hydrogen absorbed by the Mg alloy powder was measured in terms of change in pressure in the vessel after every 20 seconds, thereby providing the results shown in FIG. 3. It was found from FIG. 3 that the amount of hydrogen absorbed by the Mg alloy powder reached about 6.4% by weight of the maximum amount of hydrogen absorbed after about 8 hours from the start of the hydrogenation.

[0030] (D) Releasing of Hydrogen from the Mg Alloy Powder

[0031] 0.1 gram of the Mg alloy powder resulting from the hydrogenating treatment was placed in a vessel kept at 85° C., and 5 cc of distilled water having a temperature of 85° C. was then poured into the vessel, to thereby generate a reaction represented by a reaction formula, MgH₂+2H₂O→Mg(OH)₂+2H₂. The amount of hydrogen produced was measured to provide results shown by a line a in FIG. 4. In this case, the theoretical value of the amount of hydrogen produced is 152 cc, but an amount of hydrogen corresponding to 90% or more of the theoretical value was produced five minutes after the start of the reaction. Such rapid production of hydrogen is attributable to the presence of the Fe and Ni particulates which were the catalyst metal particulates. A line b in FIG. 4 indicates a case where the same hydrogen producing process as that described above was carried out under the same conditions, except that a powder produced by subjecting a powder of pure Mg to a hydrogenating treatment was used. Comparison between the lines a and b reveals an operational effect of the catalyst metal particulates.

[0032] (Embodiment II) To produce hydrogen by the reaction of an Mg alloy power with water, an aggregate of Mg alloy particles 3 each comprising an Mg particle 1 and a plurality of catalyst particulates 2 existing on a surface of the Mg particle 1 and within the Mg particle 1 is used. The catalyst metal particulates 2 correspond to at least one selected from Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Co particulates, Zr particulates, Zr alloy particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.

[0033] In this case, the required numerical values for the content G of the catalyst metal particulates 2 in the Mg alloy powder as well as the particle size D of the Mg particles 1 and the particle size d of the catalyst metal particulates 2 are the same as those in Embodiment I.

[0034] For example, 104 mg of the Mg alloy powder in Embodiment I (Mg₉₅Ni_(3.33)Fe_(1.67)) but not subjected to a hydrogenating treatment was placed in a vessel kept at 85° C. Then, 5 cc of distilled water having a temperature of 85° C. was poured into the vessel, to thereby generate a reaction represented by a reaction formula, Mg+2H₂O→Mg(OH)₂+H₂, and the amount of hydrogen produced was measured to provide results shown by a line a₁, in FIG. 5. It was found from the line a₁, in FIG. 5 that the production of hydrogen was continued, leading to an increase in amount of hydrogen produced. A line b₁ in FIG. 5 corresponds to a case where the same hydrogen producing process as that described above was carried out under the same conditions, except that 80 mg of a pure Mg powder was used. The hydrogen production using the pure Mg powder was continued for about 1 minute after the start of the reaction, but thereafter the reaction advanced little, and hence the amount of hydrogen produced was small. It is clear from these results that an effect of promoting the production of hydrogen is provided by the catalyst metal particulates.

[0035] In each of Embodiments I and II, an aqueous solution of ions such as an aqueous solution of NaCl, an aqueous solution of CaCl₂, an aqueous solution of MgCl₂ and the like may be used as the water in place of the distilled water.

[0036] Although embodiments of this invention have been described in detail, it will be understood that this invention is not limited to the above-described embodiments, and various modifications in construction may be made without departing from the spirit and scope of the invention in the following claims. 

What is claimed is:
 1. A process for producing hydrogen, comprising reacting an Mg alloy powder with water, wherein said Mg alloy powder is a powder produced by hydrogenating an aggregate of Mg alloy particles each comprising an Mg particle and a plurality of catalyst metal particulates existing on a surface of said Mg particle and within said Mg particle, said catalyst metal particulates being at least one selected from the group consisting of Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.
 2. A process for producing hydrogen, comprising reacting an Mg alloy powder with water, wherein said Mg alloy powder is an aggregate of Mg alloy particles each comprising an Mg particle and a plurality of catalyst metal particulates existing on a surface of said Mg particle and within said Mg particle, said catalyst metal particulates being at least one selected from the group consisting of Ni particulates, Ni alloy particulates, Fe particulates, Fe alloy particulates, V particulates, V alloy particulates, Mn particulates, Mn alloy particulates, Ti particulates, Ti alloy particulates, Cu particulates, Cu alloy particulates, Ag particulates, Ag alloy particulates, Ca particulates, Ca alloy particulates, Zn particulates, Zn alloy particulates, Zr particulates, Zr alloy particulates, Co particulates, Co alloy particulates, Cr particulates and Cr alloy particulates.
 3. The process for producing hydrogen of claim 1, wherein the content G of said catalyst metal particulates is in a range of 0.1% by atom≦G≦5.0% by atom.
 4. The process for producing hydrogen of claim 2, wherein the content G of said catalyst metal particulates is in a range of 0.1% by atom≦G≦5.0% by atom.
 5. The process for producing hydrogen of claim 1, wherein the content G of said catalyst metal particulates is in a range of 0.3% by atom≦G≦1.0% by atom.
 6. The process for producing hydrogen of claim 2, wherein the content G of said catalyst metal particulates is in a range of 0.3% by atom≦G≦1.0% by atom.
 7. The process for producing hydrogen of claim 3, wherein the content G of said catalyst metal particulates is in a range of 0.3% by atom≦G≦1.0% by atom.
 8. The process for producing hydrogen of claim 4, wherein the content G of said catalyst metal particulates is in a range of 0.3% by atom≦G≦1.0% by atom.
 9. The process for producing hydrogen of claim 1 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 10. The process for producing hydrogen of claim 2 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 11. The process for producing hydrogen of claim 3 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 12. The process for producing hydrogen of claim 4 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 13. The process for producing hydrogen of claim 5 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 14. The process for producing hydrogen of claim 6 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 15. The process for producing hydrogen of claim 7 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm.
 16. The process for producing hydrogen of claim 8 wherein the particle size D of said Mg particles is in a range of 1 μm≦D≦500 μm, and the particle size d of said catalyst metal particulates is in a range of 10 nm≦d≦500 nm. 